1. Field of the Invention
The present invention relates to a device for centering and guiding rotation of a shaft, in particular in a turbine engine.
2. Description of the Related Art
In general, a turbine engine shaft is centered and guided in rotation by two support means, respectively located upstream and downstream, one of the support means possibly comprising two rolling bearings mounted beside each other.
In the art, when a bearing for guiding the shaft has only one rolling bearing, the guide bearing is commonly said to be a “simplex” bearing and is a roller or ball bearing, for example, that is carried by a rigid annular support extending around the shaft.
When a guide bearing has two rolling bearings, the guide bearing is commonly said to be a “duplex” bearing and it generally comprises a roller bearing and a ball bearing.
The ball bearing of the duplex bearing is carried by an annular support possessing a certain amount of flexibility so that it deforms in operation and allows the ball bearing to move off-center in the event of an unbalance, thereby enabling the roller bearing to take up the radial loading.
The roller bearing is carried by an annular support that also preferably presents a certain amount of flexibility in order to avoid dynamic problems. Nevertheless, in order to ensure that the roller bearing can take up the above-mentioned radial loads, the flexibility of the support for the ball bearing must be at least three times greater than the flexibility of the support for the roller bearing.
When both of the bearing supports are flexible, an oil film compression damper is generally arranged around the roller bearing. The damper has an oil-filled annular space that is defined by a portion of the roller bearing support and by a rigid annular element surrounding said portion, the space being closed axially by sealing rings that are free to rotate in annular grooves in the support portion and that co-operate in leaktight manner with an inner cylindrical surface of the rigid annular element.
In the prior art, the supports of the roller bearing and of the ball bearing are arranged one behind the other and they are fastened to each other by nut-and-bolt type means. A device of this type is relatively bulky, in particular in an axial direction, thereby preventing it from being mounted in an engine of small size.
Furthermore, in order to present flexibility, each bearing support includes an annular portion that is elastically deformable. Any increase in the flexibility of a bearing support may in particular result in lengthening the deformable annular portion of the support, thereby nevertheless increasing the axial bulkiness of the device and possibly diminishing the mechanical strength of the deformable portion of the support.
Furthermore, the effectiveness of the oil film compression damper is a function in particular of the ratio of the length of the above-mentioned oil-filled space to its radius. The greater this ratio, the greater the effectiveness of the damping. In other words, it is preferable for this space to be long and to have a radius that is relatively small so as to increase the effectiveness of the damping. Nevertheless, lengthening this space likewise gives rise to an increase in the axial bulkiness of the device.